<?php
//接口***********(作为了解)
interface Db{
    public function connect();
    public function close();
    public function query($sql);
}
class DbMysqli implements Db{
    public function connect(){
        echo 'mysqli 连接';
    }
    public function close(){
        echo '关闭';
    }
    public function query($sql){
        echo "查询{$sql}";
    }
}